In-Situ Heating: Watching Grains Coarsen

Heat a fine-grained microstructure and watch it evolve live under the microscope, the way an in-situ heating stage lets you observe it. Grain boundaries show as bright lines; as the temperature rises they migrate and the smallest grains are consumed by their neighbours. Grain growth is thermally activated, so raise the temperature, then press Heat.

700 °C
Interactive diagram: a polycrystalline microstructure under an in-situ heating stage. As temperature and annealing time increase, grain boundaries migrate and small grains are absorbed into larger ones, so the average grain size grows and the grain count falls.
Stage temperature
700 °C
Relative mean grain size
1.0×
Grains in view
180
The physics. Boundaries carry energy, so a polycrystal lowers its energy by reducing total boundary area: large grains grow and small ones vanish. Growth follows a parabolic law, ⟨D⟩ⁿ − ⟨D₀⟩ⁿ = k·t, with k = k₀·exp(−Q/RT) — thermally activated, so it is fast when hot and frozen when cold.
Illustrative material model — the temperature scale and rates shown are model choices, not universal values; the applicable scale is material-dependent.